1. Field of the Invention
The present invention relates to the control of data communication based on a distributed control system in a computer network wherein various sorts of networks and terminals are connected.
2. Description of the Related Art
Heretofore, the Internet has been chiefly made up of comparatively uniform networks (in other words, networks whose properties such as transmission rates are substantially the same). By way of example, a private LAN in an enterprise or a university has employed Ethernet cable of 10 MHz, and individual organizations have been coupled by dedicated lines of 1 MHz or so. With the spread of the utilization of the Internet, however, various sorts of networks and various sorts of terminals have come to be connected. Concretely, networks of comparatively narrow bandwidths based on radio systems or the dial-up PPP (Point-to-Point Protocol) have increased in addition to the private LANs. Herein, the radio networks differ from the conventional networks, not only in the narrow bandwidths, but also in mobile serviceabilities. Regarding the terminals, whereas desktop type terminals have hitherto formed the mainstream, personal computers of notebook type (Laptop type) and portable terminals being still smaller in size and lighter in weight have recently come into wide use.
The offer of WWW (World Wide Web) contents on the Internet in the prior art has been premised on the use of the networks and terminals which are uniform to some extent. That is, the contents have been offered to any of the networks and any of the terminals quite similarly (without considering differences in the transmission rates of the networks or differences in the processing capabilities of the terminals).
Although there has heretofore been a technique for controlling data between two points, for example, between the terminal and a server, there has not been any technique for controlling data among many points distributed within the network. The technique for the data control between the two points is stated in, for example, Japanese Patent Application No. 08-036095.
The prior art has the problem that, when the narrow-band network such as radio network is used, a long communicating time period is required for sending out data of comparatively large size such as image data. Another problem is that, when the portable terminal or the like is used, an image sent in cannot be entirely displayed. Still another problem is that, since the uniform networks are assumed, wasteful data which cannot be displayed are caused to flow through the networks in large quantities.
Moreover, the prior art has the problem that, in the network using the radio system, the line utilization factor of the network worsens, so the frequency resources thereof are wasted.